Excerpt from Journal of the British Dental Association, Vol. 23: A Monthly Review of Dental Surgery; January to December, 1902
Fig. 7. - Photograph of transverse section of shell of Pinna.
Shown in the light spaces. These dots are not Shown, you will see, in the outer spaces where the sexagonal fields, as well as the appear ance of inter-spaces are quite clear. Now there is a very curious fact in this connection which I ask you to observe. Photographs of transverse sections of enamel rods in critical focus Show a dotted appearance very similar to the secondary markings on this diatom. These dots I have described as representing the transverse sections of calcified plasmic strings as shown in the ameloblasts, but Dr. Walkhoff says that the enamel prism is grainless or structureless, precisely as the outer or out-of-focus region of spaces in the Trice ratium appear to be. I therefore conclude that Dr. Vvalkhoif, not withstanding his theoretically critical attitude, has not succeeded in getting a critical field of vision in his microscope. I Shall make this point plainer to you presently. It would have served Dr. Walk hoff's purpose much better if he had used a transverse section of the Pinna shell (fig. Here the interprismatic substance is very much finer and in an ordinary specimen it might easily appear that the prisms lie in actual contact, particularly as they have sharply angular outlines. But decalcification and also the use of certain staining agents demonstrate that the prisms are actually separated by a discrete substance. It is to be noted that Dr. Walkhoff discourages the use of acids in the treatment of enamel. Here, again, it may be that acids prove too much. My advice to the student always has been, use all methods that are given for your investigations and invent new ones if you can, if your object be to reach a point approximating the truth rather than the bolstering up of a theory. To those who are especially interested in the technique of photomicrography I may say that the Triceratium is a very easy diatom to get a critical photograph of. It is a very unimportant test for perfection of technique. The photographing of Pleurosigma angulatum at diameters (fig. As Shown in the accompanying illustration, is a much more critical test of the perfection of the optical apparatus used.
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